The invention relates to an apparatus for regulating the operation of a plant for the making of extruded products, especially synthetic plastic products or the like, which comprises an extruding tool and a calibrating tool that follows in the direction of material flow, with a measuring head for contact-free optical monitoring of a pileup of material or a swelling of material between the extrusion nozzle and the calibrating tool, the measuring head comprising spaced-apart confronting light emitting and light receiving surfaces at least the latter of which is adjacent the ends of a plurality of light conducting elements.
For the making of extruded products, one employs extruding tools for example in the form of an extruder with associated extruder nozzle. The material flow which issues from the extruding tool is advanced to a calibrating tool which determines the ultimate external shape of the extruded product. As a rule, the calibrating tool can be provided with an opening the cross-section of which corresponds substantially to that of the extruder nozzle or is somewhat smaller in order to ensure the establishment of a shaping effect. A swelling of material in the region of the orifice of the extruder nozzle and a pileup of material ahead of the calibrating tool take place in the space between the extruder nozzle and the calibrating tool.
The subject of the invention serves for optical monitoring of such swelling or such pileup for the purpose of regulating the operation of the making plant.
Downstream of the calibrating tool, there is normally provided a cooling device and a device for withdrawing the extruded product. Firstly, the development of the swelling of material or of the pileup of material ahead of the inlet to the calibrating tool can be regulated on the basis of velocity at which the extruding tool is operated; as a rule, it is possible to regulate the rotational speed of the extruder screw in a nozzle type extruder. Secondly, it is possible to influence the speed of operation of the withdrawing unit. In both instances, it is necessary to ascertain the actual extent of swelling of material or of the pileup of material ahead of the inlet of the calibrating tool and compare it with a predetermined reference value for the swelling of material or the pileup of material in order to obtain in this manner a regulating signal. German Offenlegungsschrift No. 24 33 242 discloses an apparatus for ascertaining the actual pileup of material in front of the inlet of a calibrating tool wherein a mechanical scanning of the extruded product issuing from the extruding tool takes place. German Offenlegungsschrift No. 32 34 126 proposes a contact-free optical monitoring of the pileup of material according to which an edge of the extruded product is located in the path of radiation between a light emitting surface and a light receiving surface ahead of the calibrating tool, and a measurement of absorption of light by the extruded product takes place. It was also proposed already to form a light emitting surface by a plurality of light conducting fibers which terminate at the surface and serve to convey light from a remote light source, and to further cause the ends of a plurality of light conducting fibers to extend to a light receiving surface by way of which the incident light reaches a photodetector. In this connection, the term light is intended to embrace electromagnetic radiation in the visible and neighboring ranges of the spectrum. It is preferred to utilize infrared radiation which can be detected by a photodiode with the interposition of a filter, if necessary. The light conducting fibers which are employed can constitute glass fibers.